The invention relates to the method for operating a hybrid drive system for a traction drive for a motor vehicle.
DE 100 13 597 A1 describes a hybrid drive system which, inter alia, can be used as a traction drive for a motor vehicle. An internal combustion engine is provided as the vehicle traction motor, and the electrical power produced in a fuel cell is used to drive a drive electric motor.
DE 199 13 794 A1 describes another hybrid vehicle with a fuel cell drive and an internal combustion engine drive. The internal combustion engine is connected to a vehicle drive train via a clutch, and the fuel cell feeds an electric motor which can be coupled to the drive train. The internal combustion engine drive is used as the drive for the vehicle in a starting phase, until the fuel cell drive has heated up, to ensure immediate readiness for driving. In the starting phase, the internal combustion engine drive is also used for heating the fuel cell drive to operating temperature. For this purpose, the exhaust gases from the internal combustion engine are passed along the fuel cell, and the fuel cell and the internal combustion engine are connected to a common cooler. After reaching the operating temperature for the fuel cell drive, the drive power for the vehicle is provided solely by the fuel cell drive or, when a relatively high powered demand is made, together with the internal combustion engine drive.
WO 99/19161 describes a further hybrid vehicle which is driven by a combination of a fuel cell and a gas turbine. An electric motor is provided as the traction motor, and is connected to the fuel cell and to a generator of the gas turbine. The fuel cell and the gas turbine are designed such that approximately half the achievable vehicle power is provided in the form of electrical power via the fuel cell. When the power demands on the vehicle are below the maximum fuel cell power, the drive power is provided by the fuel cell and by the gas turbine, which is operated with the fuel cell exhaust gas. When a higher power demand is made, the gas turbine is additionally operated with hydrocarbon fuel, in order to increase the power. The heat from the gas turbine exhaust gas is used by means of a heat exchanger to preheat the supply air to the fuel cell and to the gas turbine.
WO 98/40922 describes a hybrid power production system having a fuel cell and an internal combustion engine. Hydrocarbon fuel is first of all split, in a pyrolysis reactor, into a fuel component containing hydrogen and a remaining fuel. The fuel cell is operated with the component containing hydrogen, and supplies the power for the electric motor. The remaining fuel is provided as drive fuel for the internal combustion engine. The work carried out by the internal combustion engine is provided as mechanical power, or is supplied by means of a generator as electrical power to the electric motor. The exhaust gas heat from the internal combustion engine is used for heating the pyrolysis reactor and for gasification of the hydrocarbon fuel. The hybrid power production system is intended for driving motor vehicles.
DE 199 34 790 A1 describes a drive system for motor vehicles, in which an auxiliary power drive is connected in parallel with an internal combustion engine. This can also provide the drive for the vehicle in the low load range.
Furthermore, a hybrid drive apparatus for vehicles having a fuel cell and internal combustion engine drive has been proposed in a patent application, which was not published prior to the present application, with the file reference DE 100 46 690.7. The hybrid drive apparatus has at least one fuel cell, one internal combustion engine, one generator, one electric motor and a common cooling device for the fuel cell and the internal combustion engine. The electric motor is intended as a traction drive and is supplied with power by means of the generator from the fuel cell and/or the internal combustion engine. The internal combustion engine, the fuel cell and the cooling device are thermally conductively connected to one another by heat conduction means, and control means are provided via which the flow of heat from the internal combustion engine to the cooling device and/or the fuel cell, of heat from the fuel cell to the cooling device and/or to the internal combustion engine, and/or of heat from the cooling device to the internal combustion engine and/or the fuel cell are/is controlled.
All the drive systems, as described above, use the high efficiency potential of the fuel cell in order to create a drive which is as efficient as possible. However, the fact that motor vehicles are most frequently used in city traffic, that is to say that they are operated in the partial load range, is frequently overlooked. Fuel cells, which are still very expensive at the moment, admittedly have a very high efficiency especially in the partial load range, but the full potential of such a drive is generally not made use of.
An object of the invention is thus to provide a method for operating a hybrid drive system for a traction drive for a motor vehicle, which allows good fuel consumption in the city cycle and in this case can be designed to be comparatively cost-effective.
Based on a method according to the invention, the output power of the electrical auxiliary drive unit is designed such that it can cover the mean traction power in typical city driving cycle, for example in the NEFZ city cycle or in the FTP75 city cycle. The electrical auxiliary power unit in this case feeds the traction battery continuously during operation, and both the capacity and the maximum possible power output of the traction battery are designed such that it can supply the electrical traction drive with its high accelleration demands in normal city traffic. This therefore means that the traction drive is supplied exclusively via the electrical auxiliary power unit at the medium traction power level in city traffic. As soon as the power which is required for the traction drive increases, an additional component of power is provided from the traction battery. When the power required for the traction drive is below the maximum possible power from the electrical auxiliary power unit, this will feed its excess power into the traction battery to recharge it.
When the power demands from the traction drive, for example during operation with a trailer with the heavy load and/or on gradients, rises above the total of the maximum possible power output from the auxiliary power unit and the energy storage device or traction battery, the internal combustion engine is connected, in order to compensate for the power deficit. This also occurs when the energy content of the electrical energy store falls below a limit value.
In order to allow the internal combustion engine to be connected as quickly as possible, the entire hybrid drive system may be operated, for example, via thermal management, according to application DE 100 46 690.7 (or the file reference 100 46 690.7), as has already been mentioned, which application is attached to this application and incorporated by reference herein in its entirety.
With a hybrid drive system it is possible to achieve fuel consumptions in the upper class of cars which correspond to an energy equivalent of less than 5 litres of gasoline over a distance of 100 kilometres.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.